This invention relates generally to methods and system for binarizing bar codes, and, more particularly to binarizing bar codes in the presence of noise.
Bar code symbols, formed from bars that are typically rectangular in shape, are used in a variety of applications ranging from product identification to the sorting of mail. Various optical scanning systems have been developed for acquiring an image from a bar code symbol, see, for example, the system described in U.S. Pat. No. 5,969,325. Binarizing in OCR systems, as described by Wu and Manmatha (V. Wu, R. Manmatha, Document Image Clean Up and Binarization, available at http://citeseer.nj.nec.com/43792.html) is traditionally performed with a multi directional Global threshold method. Under such a binarization method, the results obtained when the bar code is obscured by noise can be difficult to decode.
Many difficulties are encountered in detecting bar codes in the presence of noise, such as the noise caused by ink smearing, when global binarization methods are used.
Several adaptive binarization methods have been proposed (see, for example, Ø. D. Trier and T. Taxt, Evaluation of binarization methods for document images, available at http://citeseer.nj.nec.com/trier95evaluation.html, also a short version published in IEEE Transaction on Pattern Analysis and Machine Intelligence, 17, pp. 312–315, 1995.). Such proposed adaptive binarization algorithms are in general complex, difficult to implement, and, therefore, have not seen widespread use.